Set 4 introduces four new graphemes, with 36 new decodable words suggested. For the first time, some of the suggested words contain two syllables, such as pocket, sunset etc., which some young children might find too difficult at this stage. Personally, I would leave these out if they cause problems.
At this stage, it is more important for children to experience success at sounding out short words. Their ability to decode longer words will improve as their short term memory develops. At this point, two "tricky words" (not fully decodable at this stage) are taught: the and to.
ck - kick, sock, sack, dock, pick, sick, pack, ticket, pocket
e - get, pet, ten, net, pen, peg, met, men, neck
u - up, mum, run, mug, cup, sun, tuck, mud, sunset
r - rim, rip, ram, rat, rag, rug, rot, rocket, carrot